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Adam Tucker: Triggering Brexit: A Decision for the Government, but under Parliamentary Scrutiny

Adam TuckerWhat more, if anything, is needed to translate the result of the referendum into actual exit from the European Union? This question, which hardly featured in public discussion before the poll, is now the subject of a fundamental public controversy.

For the withdrawal process to begin, Article 50(1) of the Treaty of Lisbon requires a decision to leave the EU to have been made according to our own “constitutional requirements” (règles constitutionnelles in the less awkward French version of the text).  So what counts as a decision to leave, and therefore as an event capable of triggering the withdrawal mechanisms in Article 50, is a question of domestic constitutional law. Three understandings of what would count as such a decision have attracted support in recent days. This post summarises those three positions before articulating and defending a fourth, hitherto neglected, possibility. I argue that the decision must be made under the statutory power created in section 2(2) of the European Communities Act 1972. My proposal has the twin advantages of being firmly anchored in authoritative legal materials and securing a further (and in my view desirable and appropriate) round of Parliamentary scrutiny when the decision is finally made.

(i) The Story So Far

First, there are signs that some on the continent have adopted the view that the referendum itself counts as the decision to leave. In their joint statement last week, the Presidents of the European Council, Commission and Parliament referred to the referendum result as a “decision” and invited the UK government to launch negotiations under Article 50 “as soon as possible”. And yesterday, the European Parliament adopted a text asserting that it is “the outcome of the referendum” which must be notified (immediately) to the European Council in order to launch the two-year withdrawal procedure provided for in Article 50.

This is plainly wrong. Under the United Kingdom constitution, the referendum does not count as a decision. It does not (unlike, for example, the referendum on the Alternative Vote in 2011) even oblige any other actor to make a decision. This point is often made by describing the referendum as “merely advisory” or “not binding”. Something more is needed, constitutionally speaking, before the decision to leave the European Union will truly have been made.

Two more plausible possibilities have dominated the domestic discussion.  The conventional position has been defended by Mark Elliott, Carl Gardner and David Allen Green and is apparently presupposed in David Cameron’s approach to the issue. They argue that the decision to withdraw is within the government’s inherent prerogative power to conduct foreign affairs. On this understanding, whilst a decision is essentially politically inevitable it will be the government (in practice, the next Prime Minister) who will decide when and how the formal decision is made, without further scrutiny or any other kind of constraint.

Support is now emerging for a third view, according to which the prerogative does not extend to making the decision to exit the EU, and primary legislation would therefore be required to give effect to the outcome of the referendum. This view has been defended forcefully by Nick Barber, Tom Hickman and Jeff King and, for different reasons, by TT Arvind, Lindsay Stirton and Richard Kirkham. It has attracted some heavyweight support, including from Sir Stephen Sedley (in comments on this blog) and Lord Lester (in a letter to The Times). I think it is wrong: the executive does have the power to take the decision to leave the EU, but that power is not grounded in the prerogative:

(ii) The European Communities Act 1972

None of the three positions discussed above envisage the existence of a statutory answer to the question. But there is one. Section 2(2) of the European Communities Act 1972 provides (in the salient part) that:

any designated Minister or department may … make provision—

(a) for the purpose of … enabling any rights enjoyed or to be enjoyed by the United Kingdom under or by virtue of the Treaties to be exercised

Prior to Article 50, no Treaty right to leave the Union existed. The options which did exist either required unanimous agreement (treaty renegotiation) or were messy, uncertain and non-consensual (violation of Union obligations and possible eventual expulsion). Neither genuinely constituted withdrawal from the Union, which is why Article 50 was passed: Member states are now entitled to negotiate to withdraw on terms agreed to by only a qualified majority or (failing that) to withdraw unilaterally if no such agreement is reached within two years.

So now the United Kingdom enjoys, by virtue of the Treaty of Lisbon, two parallel novel rights: the right to pursue an orderly withdrawal even against the wishes of some other member states, and the right to withdraw unilaterally. But they can only be exercised once a decision to leave has been made (and notified). It follows that the decision to leave comes within the terms of section 2(2):  it would be (in the 1972 statute’s unwieldy language) a decision for the purpose of enabling rights enjoyed by the United Kingdom to be exercised. In summary, section 2(2), a domestic statutory provision enacted by Parliament, provides a constitutional grounding for an executive (but not prerogative) power to make the decision to leave the EU under Article 50.

(iii) Two Consequences of the Argument

This has two important and inter-related consequences for the way the decision will be made. First, the existence of this statutory power to trigger withdrawal precludes the use of the prerogative power to pursue foreign affairs in this instance. The government has no choice; it must use the statutory power contained in the 1972 Act. Secondly the decision will be subject to the requirements of form and scrutiny to which that power is subject.

The relationship between apparently overlapping prerogative and statutory powers is governed by the test in Attorney-General Appellant v De Keyser’s Royal Hotel [1920] A.C. 508.  Lord Atkinson articulated that test (and its rationale) as follows (pp. 539-540, my emphasis):

[I]t would be useless and meaningless for the Legislature to impose restrictions and limitations upon, and to attach conditions to, the exercise by the Crown of the powers conferred by a statute, if the Crown were free at its pleasure to disregard these provisions, and by virtue of its prerogative do the very thing the statutes empowered it to do.

… such a statute … abridges the Royal Prerogative while it is in force to this extent: that the Crown can only do the particular thing under and in accordance with the statutory provisions and that its prerogative power to do that thing is in abeyance … after the statute has been passed, and while it is in force, the thing it empowers the Crown to do can thenceforth only be done by and under the statute, and subject to all the limitations, restrictions and conditions by it imposed, however unrestricted the Royal Prerogative may theretofore have been.

This means that if a statutory power is subject to more onerous conditions than the equivalent prerogative power, the executive cannot use that prerogative. The prerogative power to manage foreign affairs is thus superseded by the statutory power in section 2(2) to the extent that the 1972 Act imposes conditions on the exercise of that power.

Schedule 2 Para 2 provides that the Power to make an order under section 2 “shall be exercisable by statutory instrument”. Those statutory instruments “shall be subject to annulment in pursuance of a resolution of either House”, unless a draft has “been approved by resolution of each House of Parliament”. These conditions mean that the test in De Keyser’s is met and the decision cannot lawfully be made under the prerogative.

The conditions on the use of the section (2)2 power ensure a degree of formality and scrutiny when the government decides to trigger Article 50. It is hardly conceivable that the government would risk making a decision which would be vulnerable to subsequent annulment by a resolution of just one House. So it is almost certain that the statutory instrument making the decision to leave the EU would be presented for approval to both Houses. And it is fair to expect that in this instance, this is a responsibility that the Houses would take seriously, with the result that the decision to leave the EU would be the subject of a further round of effective debate in both Houses (although I have previously expressed some reservations about the rigour of that process). Successful passage following sufficiently rigorous deliberation would allow the decision to attain a level of legitimacy which would not be possible through direct use of the prerogative. On the other hand, if either House rejected the draft statutory instrument, then there would be an appropriate foundation for resort to primary legislation, moves toward the dissolution of Parliament and a general election, or both.

(iv) Conclusion

To summarise my argument:

(1) The European Communities Act 1972 gives ministers the power to make provision for the exercise of Treaty rights enjoyed by the United Kingdom.

(2) Article 50 creates such Treaty rights.

(3) Therefore the 1972 Act gives ministers the power to make provision for the exercise of the Article 50 rights.

(4) Under the rule in De Keyser’s Royal Hotel, this statutory power supersedes the equivalent prerogative power

(5) The exercise of this statutory power is subject to Parliamentary scrutiny.

Article 50(1) is very demanding on Member States; it presupposes that they have rigorous domestic procedures in place so that decisions to leave the Union can be legitimately made. This post has argued that we do have such procedures in place and that the constitution requires that they are followed.

Adam Tucker is Senior Lecturer at Liverpool Law School.

(Suggested citation: A. Tucker, ‘Triggering Brexit: A Decision for the Government, but under Parliamentary Scrutiny’, U.K. Const. L. Blog (29th Jun 2016) (available at

28 comments on “Adam Tucker: Triggering Brexit: A Decision for the Government, but under Parliamentary Scrutiny

  1. Christopher Gough
    June 29, 2016

    If the route to ‘trigger’ Article 50 could be by SI rather than an Act of Parliament, presumably scrutiny of the SI would be by both houses of Parliament i.e. an affirmative resolution procedure would be likely to be applied?

    If that is the case and the scrutiny took place in the current Parliament, the level of euroscepticism among MPs would be likely to mean that the SI would have as ‘rocky’ a road as any Bill before them for consideration?

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  3. kyoto2
    June 29, 2016

    I was convinced, until I checked Schedule 2 to the Act. “(1)The powers conferred by section 2(2) of this Act to make provision for the purposes mentioned in section 2(2) (a) and (b) shall not include power— … (c)to confer any power to legislate by means of orders, rules, regulations or other subordinate instrument, other than rules of procedure for any court or tribunal;”. Filing an A50 notification is an act of legislation as it repeals statute law (as already argued re Royal Prerogative).

    • dgareth
      October 2, 2016

      Schedule 2 certainly complicates matters but does the limit it places on Orders in Council refer only to the powers provided by section 2(2) or also to other sources of royal prerogative?

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  5. Stephen Griffin
    June 30, 2016

    Personally, I find the argument in this article extremely compelling. I know that there is some strength of view behind the argument that an article 50 notice is some kind of statutory repeal (Lord Pannick has endorsed this today), therefore requiring a fresh Act of Parliament, but I prefer this argument, as it recognises that leaving the EU is a right for a member state under the treaties, and not inconsistent with those treaties. It is also consistent with arguments of parliamentary sovereignty, indeed it argues that parliament has already legislated for how rights such as article 50 should be exercised.

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  8. Paul Sevcik
    July 1, 2016

    These thoughtful articles regarding Brexit and trigerring the related Article 50 are really amazing. I just don’t understand why they are all being written after the vote has already been made? All these speculations and issues regarding Brexit on this website should have been made conclusive before the vote. The ruling elite should have had all these constitutional dilemmas solved beforehand and afterwards reflected in their Vote Leave campaign.

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  10. Clan Donald
    July 4, 2016

    Hi Adam,

    Perhaps unfortunately, there is an almost certainly fatal weakness in your argument.

    From your statement of ‘overlapping powers’ I will continue on the basis that you accept that a Prerogative power to ‘decide’ exists (your argument then being that this is ‘trumped’ and rendered ‘out of bounds’ by the combination of the ’72 Act and de Keyser’s etc).

    In the broadest sense, the 1972 Act and relevant sections are themselves ‘enabling’ legislation ‘may make provision’, permitting the Crown and Ministers to introduce secondary (‘legislative’) schemes (subject to the procedural requirements), where the Crown (etc.) would otherwise not have the legal power to do so.

    Assuming, as you agree, that an otherwise legitimate Prerogative power does in fact exist, that then, is not the case here.

    The Crown simply does not have to, legally, ‘make provision’ for itself to make the (pre Art 50-trigger) ‘decision’, or in practical terms, in the post referendum (Act) situation, draw up any scheme empowering itself (with Parliamentary consent) to make the relevant order. Obviously it could (i.e. ‘may’) do so, but if, and only if it did so, would that narrow area then be ‘ring-fenced’ from any competing Prerogative power according to the authorities to which you refer.

    Inhope it is clear from the above that any attempt to defeat the Prerogative (legally) must be made on other grounds.

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  20. Jonathan
    September 2, 2016

    My reaction to this argument is that the powers under section 2(2) of the European Communities Act 1972 are ancillary in nature: “enabling any rights enjoyed or to be enjoyed by the United Kingdom under or by virtue of the Treaties to be exercised”. I think enabling a right to be exercised is not the same as defining what the right means in the first place. The argument seems to suggest that s2(2) could be used to define what a decision to withdraw from the EU is for the purposes of Article 50, i.e. that a statutory instrument could be made stating something like “any affirmative vote in a referendum constitutes a decision to leave the EU”.

    I think that, because there is no settled definition as to what a decision to withdraw is, s2(2) can’t be used in that context. The real issue is the lack of this definition. It may be that primary legislation is required to define and/or make the decision to withdraw. Once the decision is made s2(2) could be used to enable its use for Article 50 purposes.

  21. Kay Foulkes
    September 23, 2016

    My personal interpretation of De Keyser would be that it separates international treaties that have been incorporated into UK domestic law from treaties which have not, and only in relation to the latter can the royal prerogative be applied.

    This also fits with what Laws LJ said in Thoburn v Sunderland City Council in relation to constitutional statutes a position which has since been confirmed by the Supreme Court in R (HS2 Ltd) v SS for Transport.

    This also would mean that the Human Rights Act 1998 places the ECHR in a similar position as having been incorporated into our domestic legislation it is no longer a simple international treaty.

    The executive may have the power to extend the provisions of the EU treaties under s2(2) but this does not in my mind extend to withdrawing from those treaties without the specific approval of Parliament. Looking at Thoburn the ‘constitutional’ statutes have special protection and any action taken to undermine them needs to be stated expressly by parliament and cannot be implied.

    The 2016 Referendum Act gives no power to the executive to act on the result of the referendum, and if Thoburn and HS2 are to be followed then these constitutional statutes can only be repealed expressly. A reasonable reading of De Keyser only supports the argument that in passing the ECA 1972 that Parliament restricted the use of the royal prerogative in relation to the EU treaties.

    But them I’m only a lowly undergrad… what do I know.

  22. Sean Feeney
    October 1, 2016

    You cite no authority for your proposition that “the referendum does not count as a decision”.

    The fact that the Parliamentary Voting System and Constituencies Act 2011 has implementation provisions while the European Union Act 2015 does not raises a legal question but it does not answer it without authority binding on the courts that will hear the Brexit litigation.

    Your contention that the 2015 Act does not provide for a decision runs counter to a possible Pepper v Hart defence based on the highly probative evidence of the Bill’s Government proposer the then Secretary of State for Foreign and Commonwealth Affairs Philip Hammond at second reading of the Bill in the Commons.

    This is now not an academic point.

    The issue is raised in the skeleton argument for the People’s Challenge interest party, even though this is not the defence being run.

    See the partial publication of Court papers at:

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  27. Myhomeworkdone
    July 11, 2018

    Hi Adam, many thanks for sharing your views. The 1972 European Communities Act was the piece of legislation that brought the UK into the Europe Union: it gives EU law supremacy over UK national law. The whole idea behind Brexit was to safeguard our interests, but the way it has turned out is quite the contrary. A large amount of EU law effective in the UK currently relies on the 1972 Act. It ensures that some types of EU legislation – including treaty obligations and regulations – have direct effect in the UK’s legal system without the UK Parliament having to pass any further legislation. For example, safety standards on imported goods have been agreed at EU level and apply in every member country.

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